It is important to hold the poultry carcass in a motionless condition and in the proper position as processing operations are carried out on the carcass. If the carcass moves around or is not precisely located, the processing tool nay damage the carcass, be incapable of performing its function accurately, or otherwise cause the operation to be carried out in a manner that results in a lower yield of acceptable carcasses at the discharge end of the line.
One important consideration is the need to locate the vent end of the carcass at precisely the same point time after time, regardless of minor variations in bird size, so that processing tools such as a vent cutter, a body cavity opener and an eviscerator can carry out their repetitious movements using the vent end as a reference point. This allows the cuts to be made in the same way each and every time without penetrating too deeply into the poultry carcasses, without damaging the sensitive organs and entrails, and without removing excessive amounts of edible meat in the area where the cuts are being made. Furthermore, the motion of an eviscerating tool within the body cavity can be more effectively controlled so as to remove the viscera without damage and without leaving behind entrails that should have been removed. If the carcass is cocked, canted or off to one side of the supporting fixture, the processing tools cannot perform their intended functions.